In a substrate processing apparatus for performing predetermined processing, for example, chemical oxide removal (COR) processing or post heat treatment (PHT) processing on a semiconductor wafer (hereinafter, simply referred to as “wafer”) as a substrate, a plurality of process modules serving as processing chambers are arranged around a transfer module which is a common transfer chamber. While one wafer is transferred to one process module, the COR processing or PHT processing is performed on another wafer in another process module, thereby improving efficiency of the processing. In particular, since the COR processing or the PHT processing is a time-consuming process, two wafers are accommodated in each of the process modules, and the COR processing or the PHT processing is simultaneously performed on the two wafers.
In such a substrate processing apparatus, it is necessary to simultaneously transfer two wafers toward each process module, and thus, a transfer arm disposed within the transfer module holds the two wafers using a pick part installed at a tip of the transfer arm such that the two wafers overlap each other with a gap between the two wafers. Here, if the transfer arm holds only one wafer due to failure of delivery/reception of wafers or the like, only one wafer is loaded into each process module, so that the efficiency of the COR processing or PHT processing is lowered. Therefore, it is necessary to confirm whether the transfer arm holds two wafers before the wafers are loaded into each process module.
Accordingly, there is proposed a method of confirming whether the transfer arm holds two wafers. Specifically, a sensor including a light-emitting part for emitting laser light or red LED light and a light-receiving part is disposed in front of each process module within the transfer module. Each wafer held by the transfer arm is irradiated with the laser light or red LED light from the light-emitting part, and the light-receiving part detects whether the laser light or red LED light is blocked by the wafer, thereby confirming whether the transfer arm holds two wafers. At this time, since each wafer is obliquely irradiated with the laser light or red LED light from the light-emitting part, it is possible to confirm the presence of each wafer even though the transfer arm holds the two wafers while overlapping with each other.
Meanwhile, each process module has a stage for mounting each wafer thereon. If the wafer is not mounted at a correct location with respect to the stage, this is determined as an error and processing may be interrupted, so that it is necessary to correct a position of the wafer before the wafer is loaded into each process module. Conventionally, an orienter which is a position alignment device is provided to a loader module which is a standby transfer chamber connected to the transfer module, and the position of the wafer is corrected in the orienter. In this case, since it is necessary to reciprocate the wafer between the transfer module and the loader module, the efficiency of processing remarkably deteriorates. Therefore, it has been strongly required to correct the position of the wafer when the wafer is loaded from the transfer module into each process module.
However, in the aforementioned method, only one point on an edge of each wafer is detected by the sensor. If only one point on the edge is detected, a center position of the wafer cannot be specified so that the position of the wafer cannot be corrected.